Method of making a compact fluid actuator

ABSTRACT

A compact fluid powered actuator is constructed from a flexible tube assembled over a rigid core. The actuator includes an expansible chamber formed between the tube and the core. The chamber is bounded by naturally efficient and lowly stressed seals at the ends of the tube which tightly match the periphery of the core. This construction lends itself to mass production methods wherein a long core is assembled with a long tube enabling a plurality of actuators to be manufactured simultaneously.

United States Patent [191 Steger I METHOD OF MAKING A COMPACT FLUIDACTUATOR [75] Inventor: Donald June Steger, Corinth, Ky.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

221 Filed: Aug. 23, 1972 21 Appl. No.: 283,117

Related US. Application Data [62] Division of Ser. No. 98,775, Dec. 16,1970, Pat. No.

[51] Int. Cl... 821d 53/00, B21k 29/00, B23p 15/26 [58] Field of Search29/411, 157, 417, 157.1 R, 29/450, 445, 454; 53/39; 91/470; 92/90;

[451 Apr.- 30, 1974 [5 6] References Cited UNITED STATES PATENTS2,588,604 3/1952 Archer 53/39 X 2,972,779 2/1961 Cowley 128/349 X3,016,884 l/1962 Merriman. 92/90 3,095,641 7/1963 Siegel 29/41 13,325,138 6/1967 Connolly... 29/l57.l R 3,429,314 2/1969 EriCSon 128/349R 3,528,869 9/1970 Dereniuk 156/294 3,560,295 2/1971 Kimbrell et a1.156/294 X Primary Examiner-Charlie T. Moon Attorney, Agent, or F irm-Ronald Coffman 5 7 ABSTRACT A compact fluid powered actuator isconstructed from a flexible tube assembled over a rigid core. Theactuator includes an expansible chamber formed between the tube and thecore. The chamber is bounded by naturally efficient and lowly stressedseals at the ends of the tube which tightly match the periphery of thecore. This construction lends itself to mass production methods whereina long core is assembled with a long tube enabling a plurality ofactuators to be manufactured simultaneously.

7 Claims, 8 Drawing Figures PATENTEMPR 30 m4 SHEET 1 [IF 2 VFIGJ FIG. 2

DATEMTEBAPMO 1974 v 11807015 SHEET 2 OF 2 METHOD OF MAKING A COMPACTFLUID ACTUATOR CROSS REFERENCE TO CO-PENDING APPLICATION Thisapplication is a division of my co-pending application, Ser. No. 98,775,filed Dec. 16, 1970, now U.S. Pat. No. 3,703,853.

BACKGROUND OF THE INVENTION Bellows, pistons and diaphragms have longbeen employed as expansible chamber actuators for converting pneumaticor hydraulic energy into an output force. A typical limitation on theuse of actuators has been the cost and complexity of overcoming, or ofliving with, the problems of fluid sealing and in the case of a bellowsor diaphragm, fracture of a flexible member.

Of these three traditional actuators, the bellows provide the greatestsimplicity since it can be manufactured somewhat as a single member. Thetraditional bellows includes a plurality of so-called accordion pleatswhich enable a significant output stroke. The apex of each pleat has asmall radius bend which is subject to failure upon repeated stressing.The bellows device, while mechanically simple due to its potential onepiece construction, is rather complex from a manufacturing viewpointparticularly where small size bellows are concerned. In small sizebellows the uniformity of wall thickness will determine the reliabilityof the bellows over a long period of time. Those skilled in the artfamiliar with the techniques for molding thin complex walls of flexiblematerial and maintaining uniform wall thickness can recognize thelimitations of the bellows actuator.

My invention employs the readily manufacturable shapes of a rigidcylinder and a flexible tube to minimize the sealing and flexure problemof an expansible chamber in a simple and highly effective manner. A tubepress-fit over a cylinder of substantially equal periphery forms anatural seal which can be easily supplemented by a heat bond if desired.The reaction and support functions necessary to the actuator arecompactly provided by the internal rigid core which lends itself to asimple snap-in frame mounting like that common to some fuses of similarshape. While the construction of the tube can be varied to some extent,I prefer to employ a relatively non-elastic material that is'pre-formedinto a bulge defining the expansible chamber. Actuation of the devicethus involves only flexural deformation rather than any'significantamount of stretching. Due to the surrounding relationship of the tubewith the cylindrical core, it is possible to restrict flexure torelatively large radii of curvature and thereby minimize the tendencyfor local failure that limits the potential success of a bellows typedevice.

While the actuator that l have invented has the capabilities indicatedabove which by themselves make it a desirable and highly effectivedevice, it should be apparent that the simple shapes of tubes andcylinders can be manufactured to relatively close tolerances. Uniformwall thickness of a tube is relatively easy to obtain. Such uniformityis required to minimize stress concentrations that could cause localizedfailure. My actuator also lends itself to large quantity manufacture tominimize its basic cost. The fundamental shapes of a cylinder and a tubeenable simultaneous construction of a plurality of expansible chamberson a long rod surrounded by a long tube. These devices can later besevered into a plurality.

These and other concepts, features, and advantages of my fluid actuatorand the method of making it will be apparent to those skilled in the artfrom reading and understanding the following more specific illustrativeembodiment of my invention wherein reference is made to the accompanyingdrawings, of which:

FIG. 1 isa perspective view of a fluid actuator constructed inaccordance with my invention;

FIG. 2 is a longitudinal cross-sectional view of the actuator shown inFIG. I and taken along lines II II of FIG. 1;

FIG. 3 is a lateral or end cross-sectional view of the actuator shown inFIG. 1 taken along lines III III thereof;

FIG. 4 is a perspective view of the cylindrical core component of theactuator shown in FIG. 1;

FIG. 5 is a perspective view of the tubular component of the actuatorshown in FIG. 1;

FIG. 6 is a somewhat schematic view showing a method of making thecylindrical core component of an actuator in accordance with myinvention;

FIG. 7 is a schematic view showing a preferred method of forming thetubular component after assembly with the core component in accordancewith my invention and FIG. 8 is a schematic manufacturing view showingthe separation of a plurality of simultaneously formed devices intoindividual devices.

Referring now more specifically to the drawings, in FIGS. 1, 2, and 3there is shown a compact fluid powered actuator or device 10 comprisinga substantially rigid elongated core member that is best seen in FIG. 4.Core member 20 is surrounded by a flexible relatively non-elastic, fluidimpervious, tubular membrane or tube that is best seen in FIG. 5. Thetube 30 includes a bulge portion 31 that overlies an intermediatelypositioned recessed section 21 of the core member 20 to form aninflatable or expansible chamber 32. Fluid for inflating chamber 32 issupplied through a suitable conduit 11 within the core member 20. Thefluid is transmitted through an inlet 22 and a longitudinal bore 23 toan elongated channel portion 23a where it is applied internally to thetube 30 to cause inflation of the chamber 32. Due to the inelasticcharacter of tube 30, bulge portion 31 defines a fixed maximum volumefor chamber 32 when inflated as shown in broken lines in FIG. 2.

An output member is movably supported by a pivot axis or shaft 41connected to a mounting bracket 42. As shown in broken lines in FIG. 2,output member 40 is driven upwardly upon inflation of the chamber 32.The mounting bracket 42 is secured to a frame part 43 by a screw 44 andincludes a pair of spaced spring clip portions 45 for securely receivingthe ends of the core member 20. It will be seen that upwardly turnedportions 46 of the spring clip portions 45 will resiliently removablyreceive the core 20 in a manner similar to an elongated fuse mounting.Obviously other mounting devices can be employed with equal facility.

The details of the core member 20 are better shown in FIG. 4. The coremember 20 is essentially of oblong cylindrical lateral cross-sectionalor peripherial configuration. This cross-section, which is substantiallyuniform at opposite end sections 24; provides a flattened configurationhaving opposed primary surface portions 25 that provide a relativelylarge area compared to the 7 side or secondary surface portions 26. Therecessed section 21 has a longitudinal extent 27 that is long relativeto the width 28 of the core member 20 thereby providing a relativelylarge potential surface area to lie in projection with the bulge portion31 of the tube 30.

The recessed section 21 also has a surface configuration 21a that ismade substantially complementary to the shape of a force receivingportion 47 of the output member 40. As best seen in FIG. 2, the forcereceiving portion 47 thus snuggly fits against the bulgeportion 31 ofthe tube 30 and rests against the complementary configured surface 21a(see FIG. 3) of the recessed portion 21 to define a stable end limit orrest position. Only a single layer of uncrimped membraneof the tube 30lies between the force receiving portion 47 and the surface 21a, sinceas shown in FIG. 3, the excess material of the bulge portion 31 movesoutwardly to the side where it does not interfere with the precise restposition of output member 40.

The core member 20 can be made ofa variety of materials and by processesthat include both molding and machining. If the core member 20 is madefrom stock material including the longitudinal bore 23 which extendsthroughout the entire length thereof, then a plug 23b must be providedto seal one end of the bore 23.

The tube 30, as shown in FIG. 5, has an internal periphery that is'substantially equal to the external periphery of the core member endportions 24 to provide a tight fit therewith. It is preferable to employa relatively non-elastic, but thermoplastic material in constructing thetube 30 to enable the molding of bulge 31 after the tube 30 has'beenmounted upon the core member 20. It will be recognized however thatadvantages remain even if an elastic membrane is employed without apre-formed bulge 31.

The tube 30 is assembled with the core member 20 by moving the tube 30along the longitudinal axis 29 of the core member 20 and is naturalsealed therewith by the interference between the tube 30 and the endportions 24 of the core member 20. This natural seal can be supplementedby thermoplastic bonding at 33 through the useof a heated tool or anultrasonic device. Having assembled an inflatable device comprising thetube 30 mounted on the core member 20, the actuator is constructedsimply by plugging this device into the mounting bracket 42 shown inFIG. 1.

The fundamentally simple and com patable shapes of a cylindrical coremember and a tubular membrane enable efficient mass production of theseactuators. As shown in FIG. 6, an elongated rod of stock material 50provided with a longitudinally extending bore 51 is machined by acutting tool 60 to provide a plurality of spaced recesses 52 which areseparated by unmodified sections '53 therebetween. Having manufactured acore member with a plurality of recessed sections 52 therein, athermoplastic tubular membrane 54 is forced thereon with somewhat of apress fit..This elongated assembly then is placed in a mold 61 as shownin FIG. 7 containing a plurality of mold cavities each having a surfaceconfiguration 62 that defines the desired inflated shape of the bulgeportion 31 (see FIGS. 2 and Also the mold can contain heating devices 63for bonding the tube 54 to the core sections 53. The tubular membrane 54is heated prior to insertion in the mold to a temperature where it isthermoplastic. When the elongated heated assembly is placed in the mold61, the membrane 54 is stretched by inflation through either theapplication of pressure to the bore 51 or by drawing a vacuum in themold cavities 62. The stressed membrane thus permanently stretches to ashape defined by the mold cavity surface 62 and when cooled will remainin this configuration. As shown in FIG. 8, the molded assembly isdivided into individual fluid devices by a cutter 64 and later can befinally processed to the specific configuration desired as shown in FIG.1 for example. v

Those skilled in the art will recognize that I have disclosed a uniquelysimple but effective fluid actuator concept which can be emodied in avariety of materials and manufactured in a variety of ways. While aspecific embodiment and a specific manufacturing method have beendisclosed to enable those skilled in the art to understand and practicemy invention, it is to be recognized that various modifications can bemade without departing from the inventive concepts I have disclosed.Accordingly these concepts are to be limited only by the specificlanguage of the appended claims.

I claim:

1 A method of making a fluid operable device comprising the steps of:

providing a substantially rigid elongated core member having a recessedsection intermediate a pair of opposed end sections of equal lateralperiphery and having a bore extending through one of said end sectionsand intersecting said recessed section, providing a fluid impervious,flexible tubular membrane having a length greater than said recessedsection taken along the axis of elongation of said core member and atleast portions thereof having an internal lateral periphery that isapproximately equal to the lateral periphery of said end sections,

inserting said core member into said tubular membrane, and

plastically deforming said tubular membrane in the region overlying saidrecessed section to form a bulge.

2. A method of making a fluid operable device as defined in'claim 1wherein said step of providing a core member comprises the steps of:

providing stock material having a uniform peripherical configuration,and

removing material from an intermediate portion of said stock material toform said recessed section.

3. A method as defined in claim 2 wherein said stock material providedincludes a longitudinal bore extending the length of said stock materialand the method further comprises plugging said bore at one end thereof.

4. A method as defined in claim 1 wherein said deforming step comprises:

placing the assembled membrane and core member into a mold having a moldcavity surface portion in operative projection with that portion of saidmembrane that overlies the recessed section of said core member, heatingsaid membrane to a softening temperature,

and introducing fluid into the bore of said core member to stretch saidmembrane into contact with said mold cavity surface portion.

5. A method as defined in claim 1 comprising the further step of:

heat sealing said membrane to said core member where said membraneoverlies said core member end sections.

6. A method of making a plurality of fluid operable devices comprisingthe steps of:

providing a substantially rigid elongated core member having a pluralityof longitudinally spaced recessed sections formed in the externalsurface thereof and having a longitudinally extending bore formedtherein to substantially the entire length of the core member,

providing an elongated, fluid impervious flexible tubular membranehaving an internal lateral periphery that is approximately equal to thelateral periphery of said core member in the sections thereof betweensaid recessed sections, inserting said core member into said membrane,sealing said membrane to said core member in those sections of said coremember between said recessed sections thereof, and

severing said membrane and core member at intermediate points of saidsections between said recessed sections to form a plurality ofindividual fluid operable devices.

7. A method of making a fluid operable device comprising the steps of:

providing a substantially rigid elongated core member having a recessedsection intermediate a pair of opposed end sections of equal lateralperiphery and having a bore extending through one of said end sectionsand intersecting said recessed section,

surrounding about said core member, a fluid impervious, flexible tubularmembrane having a length greater than said recessed section taken alongthe axis of elongation of said core member and at least portions thereofhaving an internal lateral periphery that is approximately equal tothela eral PQFiPUF Y qtseiisnqflss t o n plastically deforming saidmembrane in the region overlying said recessed section to form a bulge.

1. A metod of making a fluid operable device comprising the steps of:providing a substantially rigid elongated core member having a recessedsection intermediate a pair of opposed end sections of equal lateralperiphery and having a bore extending through one of said end sectionsand intersecting said recessed section, providing a fluid impervious,flexible tubular membrane having a length greater than said recessedsection taken along the axis of elongation of said core member and atleast portions thereof having an internal lateral periphery that isapproximately equal to the lateral periphery of said end sections,inserting said core member into said tubular membrane, and plasticallydeforming said tubular membrane in the region overlying said recessedsection to form a bulge.
 2. A method of making a fluid operable deviceas defined in claim 1 wherein said step of providing a core membercomprises the steps of: providing stock material having a uniformperipherical configuration, and removing material from an intermediateportion of said stock material to form said recessed section.
 3. Amethod as defined in claim 2 wherein said stock material providedincludes a longitudinal bore extending the length of said stock materialand the method further comprises plugging said bore at one end thereof.4. A method as defined in claim 1 wherein said deforming step comprises:placing the assembled membrane and core member into a mold having a moldcavity surface portion in operative projection with that portion of saidmembrane that overlies the recessed section of said core member, heatingsaid membrane to a softening temperature, and introducing fluid into thebore of said core member to stretch said membrane into contact with saidmold cavity surface portion.
 5. A method as defined in claim 1comprising the further step of: heat sealing said membrane to said coremember where said membrane overlies said core member end sections.
 6. Amethod of making a plurality of fluid operable devices comprising thesteps of: providing a substantially rigid elongated core member having aplurality of longitudinally spaced recessed sections formed in theexternal surface thereof and having a longitudinally extending boreformed therein to substantially the entire length of the core member,providing an elongated, fluid impervious flexible tubular membranehaving an internal lateral periphery that is approximately equal to thelateral periphery of said core member in the sections thereof betweensaid recessed sections, inserting said core member into said membrane,sealing said membrane to said core member in those sections of said coremember between said recessed sections thereof, and severing saidmembrane and core member at intermediate points of said sections betweensaid recessed sections to form a plurality of individual fluid operabledevices.
 7. A method of making a fluid operable device comprising thesteps of: providing a substantially rigid elongated core member having arecessed section intermediate a pair of opposed end sections of equallateral periphery and having a bore extending through one of said endsections and intersecting said recessed sectioN, surrounding about saidcore member, a fluid impervious, flexible membrane having a lengthgreater than said recessed section taken along the axis of elongation ofsaid core member and at least portions thereof having an internallateral periphery that is approximately equal to the lateral peripheryof said end sections, and plastically deforming said membrane in theregion overlying said recessed section to form a bulge.